The present invention relates to a vehicle comprising an internal combustion engine, a motor, and a generator, and especially to control of drive force in such a vehicle.
In order to improve exhaust gas emission and fuel-cost performance, JP-A-H11-348603 published by the Japanese Patent Office in 1999 discloses a technique wherein a motor-generator and a continuously variable transmission are combined with an engine, and the output of the motor-generator and the output of the engine are controlled according to a running state or a battery state.
However, in vehicles having the above-mentioned drive system, there is little change of engine rotation speed during transient states such as acceleration, etc., and therefore a strange feeling may be given to the driver. Moreover, control of the motor-generator and the transmission is required, the equipment is complex and cost increase cannot be avoided.
The Applicant is carrying out research on a drive force control device for vehicles wherein a generator connected to the engine, and a motor connected to the drive wheel are made to function as a transmission. This device varies the engine rotation speed (=generator rotation speed) according to the running state of the vehicle so as not to impart a strange feeling by determining a target rotation speed of the generator based on a target drive torque and a vehicle speed.
This invention, which relates to such a drive control device, aims to perform appropriate drive force control when the front wheels and rear wheels of a vehicle are driven by different motors, respectively.
In order to achieve above object, this invention provides a drive force control system for vehicles, comprising an engine, a generator connected to the engine, a front wheel drive motor and rear wheel drive motor which are supplied power from the generator, and a microprocessor. The microprocessor is programmed to compute a target drive force of the vehicle based on an accelerator depression amount and vehicle speed, compute a target front wheel drive force and a target rear wheel drive force by dividing the target vehicle drive force, compute a power required to drive the generator based on the target vehicle drive force, compute the target rotation speed of the generator based on the power required to drive the generator and vehicle speed, compute a target torque of the engine based on the power required to drive the generator and rotation speed of the generator, control the front wheel drive motor and rear wheel drive motor based on the target front wheel drive force and target rear wheel drive force, and control the engine and generator based on the target engine torque and target generator rotation speed.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.